HR: 0830h
AN: GP31B-0752    [PDF]
TI: N-type self-reversal of remanent magnetization above and below room temperature carried by titanomaghemite in submarine basalts
AU: * Doubrovine, P V
EM: pavel@earth.rochester.edu
AF: University of Rochester, Dept. of Earth and Environmental Sciences, Hutchison Hall 227, University of Rochester, Rochester, NY 14627 United States
AU: Tarduno, J A
EM: john@earth.rochester.edu
AF: University of Rochester, Dept. of Earth and Environmental Sciences, Hutchison Hall 227, University of Rochester, Rochester, NY 14627 United States
AB: The possibility that cation-deficient titanomagnetite (titanomaghemite) could display N\'eel's classic N-type thermomagnetic behavior has been discussed in the literature since the late 1950's. Yet, few natural samples with this behavior have been reported. However, we recently noted partial self-reversals of natural remanent magnetization (NRM) carried by titanomaghemite in highly oxidized lavas from several sites on Detroit Seamount (northwestern Pacific Ocean, Ocean Drilling Project Sites 883, 1203 and 1204). These samples also showed the self-reversal of a partial thermoremanent magnetization (pTRM) given in a 40 $\mu$T laboratory field in the temperature range $250-350~{}^{\mathrm{o}}$C. To test for N-type behavior in these seamount rocks, hysteresis loops were measured versus temperature at the Institute for Rock Magnetism. Through the temperature dependencies of saturation magnetization (Ms), we observed that samples that did not show pTRM self-reversal had broad N-type minima, with compensation temperature below $0~{}^{\mathrm{o}}$C. One of these samples showed a N-type self-reversal of saturation isothermal remanent magnetization at low temperature. In Ms(T) curves of samples which showed the self-reversal of pTRM we observed even broader N-type minima with compensation points distributed above and below room temperature. We believe that N-type grains of titanomaghemite with compensation points above room temperature in these rocks are responsible for the partial self-reversals of pTRM we have observed. This explanation is further supported by the observation that the blocking temperatures of the self-reversed pTRM are lower than those that characterize the initial stages of titanomaghemite inversion. Further rock magnetic and compositional data, together with a comparison with theoretical calculations will be discussed.
DE: 1519 Magnetic mineralogy and petrology
DE: 1527 Paleomagnetism applied to geologic processes
DE: 1540 Rock and mineral magnetism
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting